1. Field of the Invention
The present invention relates to a light metering device adapted for use in an automatic focusing (hereinafter abbreviated as AF) camera or the like and obtaining a metered light value by the output of an AF photosensor provided with photoelectric sensor arrays of which photoelectric conversion areas in the image frame partially overlap (for example photosensor arrays with a cross-shaped photoelectric conversion area).
2. Related Background Art
In case of obtaining the measured light value on the luminance of object, from the output of a focus state detection device having a charge-accumulating photoelectric conversion device normally employed in the AF cameras, it is already known that the accuracy of light metering is deteriorated under a light source involving flicker such as a fluorescent lamp, because the calculated light value is aberrated from the average object luminance, depending on whether the charge accumulation is conducted at the peaks or bottoms of the flicker.
For resolving this drawback, the Japanese Patent Laid-open Applications Nos. 62-19824 and 62-259022 disclose a method of employing the average of plural charge accumulations, thereby avoiding the influence of fluctuation in the measured value in a single light metering operation and obtaining an averaged (accurate) measured value on the object luminance.
However, each light integrating operation requires a time for analog-digital (A/D) conversion and focus state calculation in addition to the charge accumulation time and the charge transfer time, repetition of plural integrations (four integrations in the description in the Japanese Patent Laid-open Application No. 62-259022) after the start of light metering, for the purpose of improving the accuracy of light metering. This detrimentally affects the rapid phototaking ability of the camera employing such device.
Thus, an increase in the number of integrations to be averaged, for improving the stability, deteriorates the response. Also a mere increase in the number of light metering cycles does not necessarily lead to an exact measured value, if the timing of light metering is eventually synchronized with the cycle of flicker.
Besides, the plural light metering operations and A/D conversions in a same photosensor array are an unnecessary process and have to be avoided.